In humans and other foveate animals eye movement is essential both for clear vision and for visual information processing and cognition. The overarching goal of our research is to elucidate the neural mechanisms of eye movement control for understanding etiology of oculomotor disorders (e.g., nystagmus, strabismus, etc.) in neurological diseases and developing discriminative diagnoses and effective treatments. In this R21 proposal, we are going to simultaneously measure eye position, muscle tension (MT) and motoneuron activity of the medial and lateral recti during combined eye- head gaze shifts. The proposal meets the objectives of the R21 program in two ways: [1] This will be the first time that MT of an agonist/antagonist pair will be measured during combined eye-head gaze shifts and related to eye movement and motoneuron activity; [2] We are going to test the hypothesis that innervation of the medial and lateral recti can become non-reciprocal in the presence of interactions between saccadic gaze shifting response and gaze stabilizing response. If correct, this hypothesis would cause a paradigm shift away from the gaze control models pioneered four decades ago by DA Robinson (1968, 1975, 1978), which are the basis of most current oculomotor basic science and clinical intervention. This application will provide important knowledge not only for understanding the fundamental vestibular and oculomotor neurophysiology, but also for improving the diagnosis and treatment of vestibular and oculomotor disorders in humans.